Toaster

ABSTRACT

This drop-down toaster has a bread support and a door at the bottom of each toasting compartment. The door has a series of vent holes for air convection which produces improved uniformity in the toast. The door and bread support are held closed by rollers on solenoid-controlled sliding bars. The rollers allow the door to swing open before the bread support is released, and they return the door and bread support to their normal condition automatically by a cam action. The bread support is cammed upwardly before release to dislodge bread from the toasting compartment guide wires. An electronic timing circuit is located in a base underneath and spaced vertically from the toasting section so that it is not affected by heat from the toasting section. The timing circuit is compensated in accordance with previous use rather than by sensing the temperature of the toasting compartment. That is, for any two successive toasting cycles, the second toasting cycle is made longer if the interval between the two cycles is longer and shorter if the interval between the two toasting cycles is shorter. Similarly, the second toasting cycle is dependent on the length of the preceding toasting cycle so that if the preceding toasting cycle is short, the second toasting cycle is long, and vice versa. The relay for switching current in the toaster heating elements is remote from the timer circuit board so that it can be replaced in the event of a short circuit without disturbing the circuit board.

BRIEF SUMMARY OF THE INVENTION

This invention relates to bread toasters and specifically to toastershaving low or medium output rates intended primarily for use inrestaurants, diners and cafeterias and in various institutionalfoodservice facilities, for example messhalls, galleys and the like.

There are three basic types of toaster: the pop-up toaster, thecontinuous toaster, and the drop-down toaster. In addition, othermiscellaneous types of toasters exist, such as the now obsoletedoor-type toaster.

Pop-up toasters, which are the most common toasters used in the home,are also very popular in foodservice facilities. These toasters aremechanically complex. Light-duty varieties of pop-up toasters arenotoriously unreliable. Heavy-duty pop-up toasters and well-madelight-duty machines can be quite reliable, but are usually expensive tomake and difficult to repair. The principal reason for theunreliability, high cost, and difficult repair of pop-up toasters is thelarge number of moving mechanical parts required for a workable pop-upmechanism. Another problem with pop-up toasters is that if slices oftoast are not promptly removed from the toaster when toasting iscompleted, they tend to dry out because they remain situated partly inthe toasting compartment and continue to be heated by the residual heatwithin the toaster. Pop-up toasters also require frequent cleaningbecause of bread crumb accumulation. Unless regular cleaning takesplace, crumb accumulation gives rise to maintenance problems.

Continuous toasters, i.e., toasters having continuously moving breadconveyors and in which electric heating elements are energizedcontinuously over long periods of time, are suitable only forhigh-volume use in large restaurants or in institutional foodservicefacilities. Even in these restaurants and institutional facilities,continuous toasters are wasteful of energy unless their use is limitedto peak hours.

The third basic type of toaster, the drop-down toaster, is one in whichtoast is loaded from the top as in a conventional pop-up toaster, but isdischarged from the bottom. A number of these devices have beenproposed. In most, bread is temporarily supported in position betweensets of electric heating elements by a movable bread support whichslides or pivots out of the way when the toasting cycle is completed inorder to allow the toasted bread to drop into a receptacle. Thedrop-down toaster is potentially much simpler than the pop-up toaster,and is much less wasteful of energy than the continuous toaster.Furthermore, unlike the pop-up toaster, it does not continue to heat anddry out slices of toast after toasting is completed. The drop-downtoaster also substantially eliminates problems resulting from breadcrumb accumulation. Despite these potential advantages, and even thoughnumerous drop-down toasters have been proposed, none of them has metwith substantial success. The pop-up toaster is still the most populartype of toaster for home use. In foodservice use, while the continuoustoaster has made inroads, the pop-up toaster is still widely used.Drop-down toasters are a rarity.

While it is not altogether clear why the many drop-down toastersheretofore proposed have not been successful, these proposed drop-downtoasters are subject to a number of problems which may account for theirlack of success.

Some of the previously proposed drop-down toasters have toastingcompartments in the form of vertical channels which are open both at thetop and at the bottom. Others have vertical channels with bottomclosures. Still others have both bottom closures and top closures. Wherethe channels are open both at the top and at the bottom, bread tends totoast very slowly unless large amounts of energy are used. The excessivetime required to toast a slice of bread in a device of this type makesit unsatisfactory for foodservice use. Furthermore, excessively slowtoasting of bread tends to dry it out, with the result that the toastproduced has a hard and unsatisfactory texture.

The use of a top closure on the vertical channel causes excessivebuild-up of heat in the machine. Attempts to compensate for excessivebuild-up of heat by reducing the temperature of the heating elementsresult in low productivity because of excessively long periods of timerequired for toasting.

The use of a bottom closure on the channel of a drop-down toaster speedsup the toasting process, but also gives rise to several problems. If thetoasting time is short, the bread may be satisfactorily toasted on theoutside, but not toasted inside. If a longer toasting time is used, thebread may be too dark on the outside. Thus, when a bottom closure isused on the channel of the toaster, it has been necessary to use shorttoasting times, and the resulting toast is unsatisfactory. Anotherresult of the short toasting times is a non-uniformity of the toastproduced. That is, one slice of toast delivered by the toaster may bequite different from the preceding slice. Non-uniformity also exists ina different sense in that one part of a single slice of toast may bequite dark compared to other parts of the same slice. Because oftemperature variations in the toasting compartment, it has not beenpossible to produce consistently uniform results with very shorttoasting times.

In some proposed drop-down toasters the bread was supported by a doorclosing the bottom of the toasting compartment. These toasters were notsatisfactory because they were not capable of toasting the lower part ofthe bread slice satisfactorily. Other toasters having bread supportsseparate from the door were either too complex or unsatisfactory forother reasons. In one toaster a door and a separate bread support wirewere linked together, biased by a spring in the closing direction, andheld closed by a solenoid-operated latch. When the latch was opened theweight of the bread caused the bread support wire and door to pivotdownwardly. In another toaster, the door and bread support wire werefixed together. In still another toaster, the door was held by a latch,allowed to swing downwardly when the latch was released, and returned toa closed condition manually. None of these toasters was completelysatisfactory from the standpoint of simplicity and reliability.

Most of the proposed drop-down toasters, and many of the existing pop-uptoasters use mechanical or electronic timing devices to determine thetime of residence of the bread in the toasting compartment. Atemperature sensor located in the toasting compartment is used tocompensate the timer so that, if the toasting compartment is very hot,the toasting time is shortened, while if the toasting compartment isrelatively cool, the toasting time is lengthened. The sensing devicesare typically bimetallic elements in the case of mechanical timers, andthermistors in the case of electronic timers. In either case, thetemperature sensing device is responsive to convection heating by theair within the toasting compartment whereas the bread is toastedprimarily by radiant heat. Because the temperature sensor is responsiveto convection heating, the compensation of the timer is subject to anumber of disturbing factors, particularly where the bottom of thetoasting compartment is open so that cool air can enter. For thesereasons, compensation of the timer by sensing the temperature of the airwithin the toasting chamber does not necessarily produce the desiredresult, namely uniform toast.

Another problem in drop-down toasters is that certain kinds of bread,particularly those with high sugar content, such as raisin bread andrefrigerated bread, tend to adhere to the wire guides in the verticaltoasting compartment when heated. In some cases, this may prevent thetoast from dropping out of the toasting compartment when the toastsupport pivots or slides out of the way. While this problem has beenrecognized, the proposed solution, namely a mechanism which shakes thetoast loose after the bottom support is fully opened, is complicated andnot completely satisfactory.

Another problem in conventional toasters of the type havingtemperature-compensated timers is that the timer is typically subjectedto high temperatures from the toasting compartment. These hightemperatures may affect the performance of the timer, and mayoccasionally cause its failure. This problem exists with mechanicaltimers as well as with electrical timers.

Another problem in conventional toasters using electronic timers is thatthe heating elements may occasionally become short-circuited.Short-circuiting of the heating elements is very likely to cause failureof the switching device controlling current in the heating elements.Such failure necessitates replacement of the entire electronic timercircuit.

Another problem with conventional toasters of the drop-down type is thatthe toast cools after it is dropped into the receptacle underneath thetoasting compartment. If the toast is left in the receptacle for toolong a period of time, it is no longer suitable to be served. Whilepop-up toasters tend to keep the toast warm they have a tendency to dryout the toast. Conventional drop-down toasters have no provisions forovercoming the cooling problem.

It is an object of the invention to avoid one or more of the problemsdiscussed above. The principal object of the invention is to provide atoaster having a very high degree of reliability, making it suitable forlow or medium volume service in a foodservice facility either by itselfor as an adjunct to a continuous toaster.

Among the other objects of the invention are the avoidance of drying oftoast, speed of service, ease of use, and uniformity of results. Stillfurther objects of the invention include the avoidance of cold toast,and the provision of a toaster which is structurally simple and easy torepair.

This invention addresses the problem of adhesion of raisin bread,refrigerated bread, and various other kinds of bread to the wire guidesin the toasting compartment of a drop-down toaster. The toaster inaccordance with the invention comprises a toasting compartment having anelongated horizontal cross-section and having upper and lower ends. Anopening is provided at the upper for insertion of a slice of bread.Guide means are provided within the toasting compartment for maintainingthe slice of bread substantially vertical. A discharge opening isprovided at the lower end of the toasting compartment, and releasablebread support means, within the toasting compartment, engage the loweredge of the slice of bread and temporarily maintain the slice of breadin the toasting compartment with its lower edge spaced above thedischarge opening. Means are provided for establishing a toasting cycle,and means responsive to the toasting cycle-establishing means releasethe bread support at the end of the toasting cycle, thereby causing theslice of bread to drop through the discharge opening. Means are alsoprovided for effecting an upward movement of the bread support meansimmediately before release, whereby, if bread is adhered to the guidemeans, it is forcibly dislodged. This mechanism is much simpler, andmore reliable than previously proposed mechanisms in drop-down toasters.

Still further objects and advantages of the invention will be apparentfrom the following detailed description and the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is an oblique perspective view of a toaster in accordance withthe invention having four toasting compartments;

FIG. 2 is an oblique perspective view of the bread release mechanismserving two of the four toasting compartments;

FIG. 3 is a section through a toasting compartment on a vertical planeperpendicular to the long dimension of the compartment;

FIGS. 4, 5 and 6 are schematic views of the bread support and doorrelease devices, illustrating several successive stages in the operationof the bread release mechanism; and

FIG. 7 is an electrical schematic showing the timer circuitry and theheating element control circuitry for two of the four toastingcompartments.

DETAILED DESCRIPTION

Toaster 10, as shown in FIG. 1, comprises a toasting section 12, a toastcollection pan 14 located underneath and spaced from the bottom of thetoasting section, and a control section 16 located underneath andsupporting collection pan 14. The bottom of the collection pan ispreferably spaced from the bottom of toasting section 10 by a verticaldistance at least as great as the height of a slice of bread so that,when slices of bread are dropped, they are completely free of thetoasting section before they reach the bottom of the collection pan. Thedistance is typically about 19 cm. or more.

The collection pan is removable for cleaning purposes, and may simplyrest upon control section 16.

The toasting section contains two completely independent toastingsections, each having two toasting compartments. The control sectioncontains two completely independent electronic timing circuits, eachhaving its own set of controls on the front panel. The left-hand set ofcontrols comprises a starter button 18, a pilot light 20, a timingadjustment 22, and a reset button 24. These controls serve toastingcompartments 26 and 28 in the toasting section. A similar set ofcontrols on the right-hand side of the panel serves toastingcompartments 30 and 32. The operation of the controls will be more fullyunderstood from the description of the electronic timer which appearssubsequently in this specification. Briefly, however, the toaster isoperated as follows. The timer control knob 22 is adjusted to determinethe desired lightness or darkness of the toast. Slices of bread areplaced into toasting compartments 26 and 28 from above, and starterbutton 18 is pressed. Pilot light 20 immediately comes on to indicatethat toasting is taking place. The electronic timer automaticallydetermines when the desired toasting time has elapsed. The electronictimer then simultaneously deenergizes the heating elements and triggersa mechanical release mechanism which allows the toast to drop downwardlyfrom the toasting section into collection pan 14. The toast releasemechanism is automatically reset, and the next toasting operation can beinitiated by placing slices of bread into the toasting compartments andpressing starter button 18.

One important advantage over conventional pop-up toasters which isrealized by the drop-down mechanism, is the avoidance of continuedheating and drying out of the toast. Whereas, toast must be promptlyremoved from a pop-up toaster in order to prevent it from becoming driedout by heat from the toaster, the toast dropped into collection pan 14is removed from the heat, and holds its moisture for a considerableperiod of time following the toasting operation.

If toast has remained in pan 14 for too long a time, and becomes cool,it can be reheated simply by placing it into the toasting compartmentsfrom above, and reheated by depressing starter button 18. After a shortperiod of time, e.g. 15 seconds, reset button 24 is depressed. The resetbutton turns off the heating elements, and simultaneously activates therelease mechanism to drop the now warmed toast into the collection pan.

Control section 16, being located below the toasting section, receivescomparatively little heat from the toasting section. Therefore,semiconductor circuitry, which is inherently heat-sensitive, can be usedin the control section without being adversely affected.

Electrical connections are provided between the control section 16 andthe toasting section 12 to control the heating elements and the breadrelease mechanism, which is solenoid-operated. These electricalconnections are preferably located between a pair of closely spacedpanels forming the front and back sides of the rear wall of the toaster.

The toasting section is rigidly connected to the control section by thevertical elements at the rear of the toaster. The control section servesas a base, and the vertical elements at the rear of the toaster providesubstantially the entire support for the toasting section.

As shown in FIG. 1, toast collection pan 14 is constrained againstsidewise and rearward horizontal sliding by the front panel of the rearwall and by flanges extending forwardly from the rear wall. Thecollection pan can be removed for cleaning simply by sliding itforwardly.

FIG. 2 shows the toast release mechanism serving two of the fourtoasting compartments. Another similar toast release mechanism servesthe other two toasting compartments. The toast release mechanism can bedesigned to serve any desired number of toasting compartments from oneon up. However, experience has shown that the most desirable mechanismis one which serves two toasting compartments simultaneously.

The toast release mechanism of FIG. 2 comprises a sinuous bread supportwire 34 normally lying substantially in a horizontal plane and securedto an elongated wire 36. Wire 36 pivots about its longitudinal axiswhereby support wire 34 moves from its normal horizontal planedownwardly into a vertical plane to release toast downwardly.

A short distance below bread support wire 34 is a pivoting door 38 whichalso lies normally in a horizontal plane, but which pivots downwardlyinto a vertical plane to allow bread released by bread support wire 34to drop downwardly from the toasting compartment into the collection panthrough a discharge opening.

Door 38 is preferably in the form of an elongated metal sheet having aseries of circular holes 40 evenly distributed in a line along itslength. Holes 40 serve as vent holes. The total area of holes 40 shouldbe within the range of approximately 2% to approximately 10% of thehorizontal cross-sectional area of the toasting compartment. Preferably,the total area of the holes is about 5% of the horizontalcross-sectional area of the toasting compartment. These holes serve asvent holes, allowing a restricted upward flow of air into the toastingcompartment by convection. The flow of air through the toastingcompartment removes excessive moisture from the surface of the bread inthe toasting compartment. This prevents heat from being wasted inevaporating moisture and therefore enables the bread to begin darkeningmore quickly. The flow of air through holes 40 also results in a moreconsistent temperature rise in the toasting compartment. It helps toproduce slices of bread which are uniformly toasted throughout, and alsoto produce uniformity in the sense that successively toasted slices ofbread come out of the toaster substantially in the same condition. Byallowing a restricted flow of air through the vent holes, these resultscan be produced without requiring excessive toasting times.

While the line of holes as shown in FIG. 2 is preferred, the vent holescan be provided in many alternative configurations. While it is possibleto provide vent openings in the sides of the toasting compartments anduse unperforated doors, providing vent openings in the doors isstructurally much simpler, and produces better results because it causesair to flow directly upwardly toward the bread being toasted and pastthe slice of bread on both sides.

The bread release mechanism is activated by two electrically energized,solenoid-operated linear actuators 42 and 44, which for simplicity willbe referred to as "solenoids". Armature 46 of solenoid 42 is providedwith a bracket 48. This bracket is fixed on armature 46 by a suitablescrew (not shown), and has a cylindrical projection 50 which extendsthrough a circular hole in arm 52. Projection 50 preferably consists ofa pin having a rotatable cylindrical PTFE sleeve. The rotation of thesleeve permits the solenoid and arm 52 to cooperate mechanically withoutproducing excessive wear. Similar pins and sleeves are used throughoutthe bread release mechanism. All of these PTFE sleeves, and thesolenoids as well, are protected from the heat of the toastingcompartments by suitable metal shields not shown in FIG. 2.

Arm 52 is pivoted on a stationary rod 54, and moves clockwise assolenoid armature 46 is retracted into solenoid 42. Clockwise movementof arm 52 is aided by solenoid 44, the armature 56 of which has abracket 58 with a sleeved projection extending through a hole in arm 52above pivot rod 54.

Arm 52 is forked at its upper and lower ends. The fork at the upper endof arm 52 receives a PTFE-sleeved cylindrical projection 60 on slide bar62. Bar 62 is horizontally slidable in guides 64 and 66. Bar 62 rests ona roller 68 in guide 66 and on a similar roller (not shown) in guide 64.Bar 62 slides toward guide 66 as arm 52 moves clockwise under the actionof the solenoids.

An arm 70 is secured to bread support pivot wire 36. Arm 70 is a sheetmetal element with a downwardly bent flange having a lower edge 72.Lower edge 72 has a downwardly projecting hump 74. The lower edge of thedownwardly extending flange of arm 70 rests on a sleeved projection 76which extends horizontally from slide arm 62.

As slide bar 62 moves toward the right, projection 76 engages hump 74and momentarily moves bread support wire 34 upwardly before allowing itto drop downwardly into a vertical plane. This upward motion, which willbe better understood from FIGS. 4, 5 and 6, serves to disengage thebread from the guides in the toasting compartment.

Slide bar 78 is held by guides 79 and 80, and slides horizontally overrollers 82 and 84. Bar 78 has a downwardly extending projection 86 towhich is secured one end of a return spring 88. Spring 88 is in tensionbetween projection 88 and fixed bracket 90. It urges bar 78 toward theright.

Sleeved projection 92 is engaged by the forked lower end of arm 52, andis secured to projection 86 of arm 78. Therefore, clockwise movement ofarm 52 corresponds to a leftward movement of arm 58, and an increase inthe tension in spring 88.

Bar 78 has a sleeved projection 94 extending rearwardly from a locationnear its right-hand end. Door 38 is pivoted on a rod 96 and has adownwardly extending flange 98 at its near end. The lower edge 100 ofthis flange is contoured and cooperates with sleeved projection 94 insuch a way that when bar 78 is in the rest position, as shown, door 38is held horizontal, i.e., in the closed condition. When the solenoidsare energized, and bar 78 moves to the left, projection 94 movesunderneath pivot rod 96, and allows the door to swing downwardly into avertical plane.

The right-hand bread support wire and door in FIG. 2 are operated in asimilar manner by rearwardly extending projections near the right-handends of bars 62 and 78 in a manner similar to the manner in whichsupport wire 34 and door 38 are operated.

FIG. 3 shows the relationship between the bread support wire, the doorand the principal elements of the toasting compartment. The toastingcompartment has resistance wires 102 and 104 which serve as heatingelements. These wires are supported on insulating supports 106 and 108respectively. A series of parallel toast guide wires is provided on eachside of the toasting compartment to prevent bread from directly engagingthe heating elements. One of the toast guide wires is shown at 110, andanother at 112. These toast guide wires are shaped so as not to contactthe bread along long continuous lines.

Bread support wire 34 is located near the lower end of the toastingcompartment, but between the heating elements near the lower end of thecompartment. Door 38 is located below the lowermost extent of theheating elements. Bread support wire 34 is pivoted on the right, whiledoor 38 is pivoted on the left.

The successive steps in the operation of the bread support wire and thedoor are illustrated in FIGS. 4, 5 and 6. FIG. 4 shows the support wireand door in the rest position, in which both the support wire and thedoor are situated substantially in horizontal planes.

As toasting is completed, and upon actuation of the solenoids,projection 76 begins to move toward the right, while projection 94begins to move toward the left. As shown in FIG. 5, door 38 begins acontinuous and steady opening movement, while bread support wire 34 doesnot begin its opening movement until projection 76 clears arm 70. Thisinsures that the door will be completely open before the bread supportwire is released. This action prevents jamming of the toast in the toastrelease mechanism.

In FIG. 5, projection 76 engages hump 74 on arm 70, effecting amomentary upward movement of bread support arm 34. This movement of arm34 pushes the toast upwardly, and disengages it from toast guides 110and 112 in the event that it has adhered to these guides for any reason.

Further rightward movement of projection 76 and leftward movement ofprojection 94, as shown in FIG. 6, results in the dropping of both thebread support wire and the door into vertical planes, whereby the toastis released and dropped into the collection pan.

Referring again to FIG. 2, when the solenoids are deenergized, spring 88urges bar 78 to the right. This movement of bar 78, in turn, causescounterclockwise rotation arm 52, and leftward movement of bar 62.Projection 94 acts against edge 100 of flange 98 to return door 38 toits closed condition. Simultaneously, projection 76 acts against edge 72of arm 70 to return bread support wire 34 to its horizontal condition.

The bread support wire and door are opened by gravity, and closed by thecamming action of bars 62 and 78. This is an extremely simple and veryreliable system for operating the bread support wire and door. There isno need for any trigger mechanism nor any complex resetting device. Themechanism is also much simpler and more reliable than a system in whichthe doors and support wires are provided with individual return springsand forced open against the action of the individual return springs. Thesystem shown in FIG. 2 can be modified to serve any desired number ofdoors and support wires without greatly increasing its complexity.

Referring to FIG. 7, a supply of alternating current is connected tolines 114 and 116. DC current for operating the electronic timercircuitry is derived through a half-wave rectifier circuit comprisingresistor 118, diode 120, capacitor 122 and regulating Zener diode 124.This circuit delivers a low DC voltage to line 126. Line 116 is a commonline for both DC and AC.

The duration of the toasting cycle (i.e. the time during which bread isbeing toasted) is determined by a timer circuit which comprises anintegrated circuit timer 128. This timer may be any one of a variety ofgeneral purpose timers such as the ICM 7555, available from Intersil.The timer comprises a three input NOR gate 130 interconnected with a twoinput NOR gate 132 to provide a bistable circuit. A first comparator 134has its output connected to one of the inputs of NOR gate 130. A secondcomparator 136 has its output connected to an input of NOR gate 132. Theoutput of the bistable circuit is derived through a pair of invertingoutput drivers 138 and 140 connected in series. A built-in MOSFET 142,gated by the output of driver 138 is provided to discharge a timingcapacitor. Its drain is connected to an input of comparator 134. Theother input of comparator 134 is connected to receive a control voltagefrom timing adjustment 22. One of the inputs of comparator 136 isconnected to receive a trigger pulse upon momentary closure of starterbutton 18. The other input of comparator 136 is connected to a resistivenetwork which holds it at a DC voltage level between the voltage in line126 and that in line 116.

The output of the timer, derived from the output of inverting driver140, is connected through a pair of Schmitt triggers 142 and 144 to thegate of an SCR 146. SCR 146 controls a relay coil 148, the contacts ofwhich operate heating elements 102 and 104 in one of the toastingcompartments, as well as another pair of heating elements in a secondtoasting compartment. Pilot light 20 is connected in parallel with theheating elements.

The operation of the timer is such that when push button 18 ismomentarily depressed, the output of driver 140 immediately goes high,and remains high for the duration of the toasting cycle as determined bythe parameters of the various timing elements, as will be discussedbelow. As soon as the output of driver 140 goes high, SCR 146 istriggered, and the contacts of relay 148 close, delivering current tothe heating elements and the pilot light. SCR 146 remains triggeredthroughout the toasting cycle by a constant DC current at its gate.

At the end of the toasting cycle, the output of driver 140 goes low, andthe output of Schmitt trigger 144 similarly goes low, removing gatingcurrent from the SCR and deenergizing relay 148.

The output of Schmitt trigger 144 is connected through resistor 146 andline 148 to the input of Schmitt trigger 150, the output of which isconnected to the gate of SCR 152. When the output of Schmitt trigger 144goes low at the end of the toasting cycle, the output of Schmitt trigger150 goes high, triggering SCR 152. SCR 152 is connected to solenoids 42and 44, which operate the bread support wires and the doors for two ofthe toasting compartments.

During the toasting cycle, while the output of Schmitt trigger 144 ishigh, capacitor 156 charges through diode 158 and resistor 160. When theoutput of Schmitt trigger 144 goes low at the end of the toasting cycle,capacitor 156 begins to discharge through resistor 162. When the voltageacross capacitor 156 becomes sufficiently low, the output of Schmitttrigger 164 goes high, causing the output of Schmitt trigger 150 to golow, thereby removing gating current from SCR 152. The result is thatSCR 152 is triggered for a predetermined duration at the end of eachtoasting cycle. The parameters of capacitor 156 and resistor 162 arechosen so that the time interval during which solenoids 42 and 44 areoperated is sufficient to allow toast to drop out of the toastingcompartments into the collection pan before the doors and bread supportwires are reset by return spring 88 (FIG. 2) to their horizontalconditions. Typically, this time interval is about one second.

The bread release solenoids may also be energized manually by pushbutton24. This pushbutton is connected to deliver a pulse to Schmitt trigger172, the output of which is connected through line 166 to the gate ofSCR 152. Pushbutton 24 can be used to release bread at any time duringthe toasting cycle or even before the toasting cycle has begun.Momentary closure of push-button 24 also resets the bistable device bycausing a pulse to be delivered to NOR gate 130 through Schmitt trigger168 and inverter 170.

The duration of the toasting cycle is determined primarily by the valueof capacitor 174 and the position of the adjustment of timing adjustment22. Capacitor 174 is connected to be charged from the output of inverter140 through diode 176, and resistors 171 and 180. An additionalcapacitor 182 is connected between the junction of resistors 171 and 180and common line 116.

When starting button 118 is momentarily pressed, the output of driver140 goes high, and capacitor 174 begins to charge. When the voltage oncapacitor 124 reaches the voltage on the wiper of control 22, the outputof comparator 134 goes high triggering the bistable device so that theoutput of driver 140 goes low and remains low. The duration of thetoasting cycle depends upon the position to which control 22 isadjusted. At the end of the toasting cycle, the output of inverter 138goes high, gating FET 142 into conduction. This causes capacitor 174 todischarge.

If it were not for capacitor 182, the duration of the toasting cyclewould be entirely dependent upon the adjustment of control 22. However,capacitor 182 also affects the duration of the toasting cycle. Capacitor182 charges through resistor 171 when the output of driver 140 is high.Capacitor 182 discharges through resistor 180 and FET 142 when theoutput of driver 140 is low. Since capacitor 182 is connected to gate142 through resistor 180, capacitor 182 does not discharge immediatelywhen the toasting cycle ends. Rather, it discharges at a slow rate.During the toasting cycle, the rate at which capacitor 174 charges isdependent upon the level of charge on capacitor 182. If capacitor 182 isalmost fully charged when a toasting cycle is begun, capacitor 174charges rapidly, and the duration of the toasting cycle is relativelyshort. On the other hand, if capacitor 182 is almost fully dischargedwhen a toasting cycle is begun, capacitor 174 will charge only slowly,and the toasting cycle will be relatively long. Thus, the duration ofany toasting cycle will be affected by the duration of the rest intervalfollowing the next preceding toasting cycle. If the rest interval, i.e.the time between toasting cycles, is long, the next toasting cycleshould be relatively long, because the toaster will be cool. If the timebetween toasting cycles is short, the toaster will be hot, and the nexttoasting cycle should be relatively short. The incorporation ofcapacitor 182 in the timing circuit accomplishes this result by makingthe timing circuit responsive to a degree to the interval betweentoasting cycles. Most significantly, this circuit accomplishes thisresult without using any thermistor or other temperature-sensitive probein the toasting compartment.

The duration of any given toasting cycle is also dependent, although toa somewhat lesser degree, on the duration of the next preceding toastingcycle. Assuming a fixed interval between two successive toasting cycles,the charge on capacitor 182 at the beginning of the second toastingcycle will be higher if the first cycle is long than it would be if thefirst cycle is short. A higher charge on capacitor 182 at the beginningof a toasting cycle shortens the toasting cycle. Therefore, for any twosuccessive heating cycles, the second cycle is shortened if the firstcycle is lengthened.

Although the duration of a toasting cycle is affected most heavily bythe duration of the next preceding rest interval and to a lesser extentby the duration of the next preceding toasting cycle, it is alsoaffected by earlier toasting cycles and rest intervals, with more remotecycles and rest intervals having a decreasingly significant effect.

Because the timing circuit makes the duration of the toasting cycledependent on the recent past usage of the toaster, the effect is similarto what occurs in toasters having temperature-compensated timers. Thepresent invention, however, has the advantage of greater simplicitybecause it eliminates the need for a temperature sensing probe, and italso has the advantage of more consistent performance, since thecompensation in the present invention is not subject to disturbingfactors such as varying temperatures of the air entering the toastingcompartments. Timer compensation in accordance with recent past usage isespecially suited to the toaster of the present invention in whichexternal air enters the toasting compartments through vent holes in thebottom doors.

Timer compensation in accordance with recent past usage is alsoespecially suited to a toaster such as the toaster of the presentinvention in which provision is made for manual resetting in order, forexample, to reheat previously toasted bread for a short period of time.The usage compensation circuit takes into account the effect of suchrelatively short toasting cycles, and modifies the operation of thetimer accordingly.

Within the control section of the toaster, the electrical circuitry isdivided into two principal parts. The timer circuit and SCRs 146 and 152are on the same circuit board, while relay 148 is physically separatefrom the circuit board. Thus, if the relay fails as a result of a shortcircuit, it can be readily replaced without disturbing the electroniccircuit and without requiring its replacement as a unit. If the relay isomitted, and one or more SCRs or triacs are used to switch current inthe heating elements these SCRs or triacs should be physically separatefrom the timer circuit board for similar reasons.

I claim:
 1. A toaster comprising a toasting compartment having upper and lower ends and an elongated cross-section transverse to the direction between the upper and lower ends, an opening for the insertion of a slice of bread, the slice of bread having parallel faces extending from one edge of the slice to an opposite edge thereof, guide means for engaging the faces of the bread slice and thereby maintaining the slice of bread in a position such that said one edge of the slice of bread is at a higher level than the opposite edge while in the toasting compartment, and a discharge opening at the lower end of the compartment, releasable bread support means within the toasting compartment for engaging said opposite edge of the slice of bread within the toasting compartment and temporarily maintaining the slice of bread in the toasting compartment with said opposite edge spaced above the discharge opening, means for establishing a toasting cycle and means responsive to the toasting cycle-establishing means for releasing the bread support means at the end of the toasting cycle, thereby causing the slice of bread to drop through the discharge opening, and means for effecting a movement of the bread support means immediately before the release thereof so that it pushes against said opposite edge of the bread slice in a direction substantially parallel to the faces of the bread slice, whereby if the bread slice is adhered to the guide means it is forcibly dislodged.
 2. A toaster according to claim 1 in which the bread support means comprises means providing a platform which normally extends substantially perpendicular to the faces of the bread slice, which is pivoted on an axis extending lengthwise of the toasting compartment along one of the sides thereof, and has an arm secured to the platform-providing means and pivoting therewith, and in which the means for releasing the bread support means comprises latch means engageable with the arm secured to the platform-providing means and normally preventing the platform from pivoting downwardly from its normal position, the latch means being movable in response to the toasting cycle-establishing means to a release positon allowing the platform-providing means to rotate in one direction about its pivot axis and release a slice of toast through the discharge opening, the means for effecting a movement of the bread support means immediately before the release thereof comprising camming means for effecting a pivoting movement of the platform-providing means in a direction opposite to said one direction as the latch means moves toward the release position.
 3. A toaster according to claim 1 in which the bread support means comprises means providing a platform which normally extends substantially perpendicular to the faces of the bread slice, which is pivoted on an axis extending lengthwise of the toasting compartment along one of the sides thereof, and has an arm secured to the platform-providing means and pivoting therewith, and in which the means for releasing the bread support means comprises latch means engageable with the arm secured to the platform-providing means and normally preventing the platform from pivoting downwardly from its normal position, the latch means being movable in response to the toasting cycle-establishing means to a release position allowing the platform-providing means to rotate in one direction about its pivot axis and release a slice of toast through the discharge opening, the means for effecting a movement of the bread support means immediately before the release thereof comprising a camming surface on the arm cooperable with the latch means to effect a pivoting movement of the platform-providing means in a direction opposite to said one dirction as the latch means moves toward the release position. 